Lt. John Everhart of San Diego Lifeguard Services briefs reporters on the case Thursday. View more videos at: http://nbcsandiego.com.

By M. Alex Johnson, staff writer, NBC News

A naked surfer washed up dead near a San Diego beach early Thursday with wounds consistent with a shark attack, authorities said.

The 42-year-old man, who wasn't further identified because his family hadn't been notified, appeared to have been attacked after he died under other unusual circumstances in the water — possibly suicide — said Lt. John Everhart of San Diego Lifeguard Services, who cited a preliminary medical examiner's report.

No shark sightings had been reported in the area, and officials didn't say what type of shark might have attacked the man. Everhart told reporters the body was found in shallow water about 250 yards from shore about 3:35 a.m. (6:35 a.m. ET) near Tourmaline Beach.

"There were wounds on the body and trauma on the body," Everhart said. "The medical examiner has indicated that the wounds are consistent with what they would expect from a shark attack."

Beyond the alarming prospect of a human-eating shark prowling the San Diego coast, other unusual factors raised questions about the case. Everhart said the man may have had an unknown medical condition or may even have set out to kill himself.

The man was naked, and there were no signs of a struggle, authorities said. His wetsuit had been carefully tied around the surfboard; neither the wetsuit nor the board showed any signs of damage when they were found well offshore.

Everhart called it odd "that someone would take their wetsuit off while they're out at sea and then tie it around their surfboard and then disappear."

"I've never seen anything like it," he said.

Tommy Calagna of Pacific Beach told NBC San Diego that he and his girlfriend saw the man sitting on his board several hundred yards out in the surf Wednesday evening — "really, really far out there, like double the distance of where the other surfers were at the time."

Calagna, a veteran surfer, agreed that it was highly unusual that a surfer would take off his wetsuit before coming out of the water.